We are not alone. Ninety percent of the cells in our bodies are not human. They are microbes — bacteria that influence our health and happiness throughout our lives.

These microbes evolved along with humanity. One type is acquired during childbirth as the baby passes through the birth canal. It specializes in digesting breast milk and prepares the baby to digest solid food. A child born by C-section does not acquire this type of microbe, which, according to the University of Chicago’s Celiac Disease Center, is probably why they develop celiac disease more often than babies born vaginally. Celiac disease causes the body’s immune system to attack the wall of the intestine when gluten is eaten. C-section babies have higher rates of other diseases that also correlate to the types of microbes in the body.

A healthy microbiome — or community of organisms — has about 1,500 species of microbes, all with specialized tasks. Most of us have far fewer. Our culture is obsessed with cleanliness, but children raised in clean environments lack microbes that would properly “train” their immune systems. As a result, such children have higher rates of allergies and asthma. Worse, a child in the United States is, on average, treated with antibiotics 10 to 20 times by age 18. Antibiotics wipe out a third of the microbiome. Some species of microbes remain dormant for years after antibiotic treatment.

I was pleased to learn that people who have pets, particularly pets that go outside and then snuggle up to their humans, have a more diverse, and therefore healthier, set of microbes than people with no pets. Gardeners and farmers have more diverse microbiomes, too.

Amazingly, some microbes trigger the production of serotonin, the neurotransmitter that creates feelings of calm and well-being. Soon we may treat depression and anxiety by altering a person’s microbiome.

Obesity is also highly influenced by the microbiome. When lean mice are given microbes from obese mice, they become obese. The reverse is also true, but only as long as the obese mice are given a healthy diet along with the microbes from their lean kin. The right diet is essential to retain the “good” microbes.

We cannot control whether we were born by natural childbirth or C-section, but we can shift the spectrum of microbes in our gut to some degree. Two Stanford scientists, Justin and Erica Sonnenburg, published a book this year titled “The Good Gut.” They explain the microbiome and, as parents of young children, they give tips and recipes to get children to eat healthy foods. I wish this book had been available when my kids were small.

A healthy microbiome requires a lot of fiber, because that is what microbes eat. Processed foods that form the “Western diet” are the worst thing for the microbiome. We need to eat fresh vegetables and fruit, legumes, nuts and seeds. Grains should be coarsely ground to get the maximum amount of fiber. In my 20s, I had a hand-turned grinder for grains and bought fresh whole wheat and berries to make cereal and bread. Hmm, where is that thing now?

Red meat should be avoided because microbes that thrive on it produce a chemical that causes strokes and heart attacks. We can increase good microbes in our systems by eating fermented foods, such as unsweetened yogurt or kefir and fermented vegetables like pickles and sauerkraut.

To my dismay, most artificial sweeteners seem to trick the microbiome into causing insulin resistance and weight gain. Stevia is the only sugar substitute that has not (yet) been shown to have this effect. Starbucks will not put Stevia in my latte — another reason to stick with the independent coffee stand near my office. To resist a cold diet soda on warm afternoons, I bought icedf tea makers for my office and home. A good glass of iced tea does the trick.

So, be good to your microbes and they will return the favor.

— Laura Wishik is the coordinator for Shape Up Vashon and teaches a class called Food for Life. She is also an attorney and mother of two.